title: Prevalence and genotypic characteristics of beta-lactamase-negative ampicillin-resistant Haemophilus influenzae in Australia.
abstract: OBJECTIVE
  To determine the prevalence of β-lactamase-negative ampicillin-resistant (BLNAR) Haemophilus influenzae in Australia and characterize the associated amino acid substitutions in penicillin-binding protein 3.
  
  
  METHODS
  Two hundred consecutive non-repeat clinical isolates of H. influenzae were collected and β-lactamase-negative isolates were screened for reduced ampicillin susceptibility using an ampicillin 2 μg disc (breakpoint <17 mm) and Etest (breakpoint ≥0.25 mg/L). All screen-positive isolates had their ampicillin MICs determined by reference broth microdilution and their ftsI genes were sequenced.
  
  
  RESULTS
  No BLNAR strains (MIC ≥4 mg/L) were found, but 5 (2.5%) low BLNAR (L-BLNAR) strains (MIC ≥2 mg/L) and 36 (18%) genetic BLNAR (gBLNAR) strains (R517H or N526K) were found. Of the gBLNAR strains, four had the R517H substitution and the remainder had N526K, while no strains had combined N526K and M377I/S385T/L389F substitutions. A number of strains with neither R517H nor N526K substitutions that did not meet the gBLNAR definition had other BLNAR-associated substitutions.
  
  
  CONCLUSIONS
  BLNAR and L-BLNAR strains are uncommon in Australia, while gBLNAR strains are more common than previously recognized.
authors.affiliation: School of Human Life Sciences, University of Tasmania, Launceston, Tasmania, Australia.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Witherden
authors.forename: Janet
authors.initials: J
authors.lastname: Montgomery
authors.forename: Barbara
authors.initials: B
authors.lastname: Henderson
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Tristram
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000667:Ampicillin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001315:Australia / Q000453:epidemiology; D006192:Haemophilus Infections / Q000453:epidemiology* / Q000382:microbiology; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000201:enzymology* / Q000302:isolation & purification; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D020125:Mutation, Missense; D046915:Penicillin-Binding Proteins / Q000235:genetics; D015995:Prevalence; D001618:beta-Lactamases / Q000096:biosynthesis*
chemical_list: D000900:Anti-Bacterial Agents; D046915:Penicillin-Binding Proteins; D000667:Ampicillin; D001618:beta-Lactamases